1. Field of the Invention
The present invention relates generally to self-cycling pump wherein valve means for alternating the discharge and re-fill stages of the pump cycle are provided directly at the pump disposed in the well. More particularly, the invention relates to a sub-surface pump provided with its own cycling means for alternately pressurizing and venting the pump, including a constantly-charged drive air supply line.
The terminology "sub-surface pump" as employed herein is intended to generally connote a pump used for lifting sub-surface fluids from subterranean depths, such as a bladder pump, a bellows pump or a gas drive pump, for example.
2. Description of Relevant Art
Mounting concerns over environmental pollution, and regulations imposed by the government, have greatly increased the use of sub-surface pumps used for groundwater sampling, recovery, and other types of operations in which sub-surface fluids are lifted from various depths to the ground surface. One type of sub-surface pump which has seen widespread use in groundwater sampling procedures is the conventional bladder pump.
Although bladder pumps are commonly used for groundwater sampling, their use in other applications has been limited. The performance characteristics of the bladder pump suffer proportionally to the depth at which the pump is disposed in the well due to limitations inherent in known arrangements. Although such limitations may not unduly impair sample collection from very shallow wells, they substantially impair sampling operations from greater depths. Such limitations also render the bladder pump unsuitable for use in other types of operations demanding relatively high flow rates, such as well purging operations.
As shown in FIG. 1, a conventional bladder pump comprises a rigid cylindrical pump body 1 having a lower inlet end and an upper outlet end. A generally cylindrical flexible bladder 5 (made of Teflon or the like) is disposed in pump body 1 so as to divide same into an outer annular actuating gas chamber 6 and an inner fluid chamber 7. A tube 8 extends through fluid chamber 7 within bladder 5, and is provided with opposite end retainers 9, 10 to which the opposite ends of bladder 5 are sealingly connected. Center tube 8 is apertured along its length to allow groundwater or other fluid to flow freely between the interior of tube 8 and the remainder of fluid chamber 7. A lower check valve 11 provided at the lower inlet end 2 permits groundwater or other fluid to pass therethrough into tube 8 and fluid chamber 7, and prevents the fluid from backflowing through the inlet from the pump interior. An upper check valve 12 permits fluid from chamber 7 to pass therethrough and be discharged through fluid conduit 13 for ultimate collection, and prevents the fluid from backflowing into the pump interior.
The conventional bladder pump is operated by alternately pressurizing and venting the gas chamber 6 so as to alternately contract and relax the bladder 5. When the pump is submerged, groundwater or other fluid flows into fluid chamber 7 via check valve 11 and tube 8 under the influence of natural hydrostatic pressure. When an actuating gas such as compressed air is supplied to gas chamber 6, the flexible bladder 5 is compressed and lower check valve 11 is closed so that fluid in chamber 7 is forced upwardly through tube 8 and check valve 12, and discharged through conduit 13. The gas chamber 6 is then vented to permit bladder 5 to relax and expand as fluid again flows into fluid chamber 7 via check valve 11 and tube 8 under natural hydrostatic pressure, to start a new cycle.
In known bladder pump arrangements, such as disclosed in U.S. Pat. Nos. 4,489,779 and 4,585,060 for example, a portable ground-level controller 30 is connected between a compressed air source and a gas actuating conduit or air tube 14 communicating with the gas chamber 6 of the bladder pump. The controller includes cycling means, which alternates between pressurizing and venting modes so as to alternately pressurize and vent the bladder pump; and timing means, which times the cycling operations of the cycling means. The cycling means typically takes the form of a three-way valve which is alternately actuated and de-actuated to produce a pulsing flow from the bladder pump. Upon actuation, compressed gas is supplied to air tube 14; upon de-actuation, the compressed air source is blocked-off and the air tube 14 is vented to atmosphere. The controller includes electronic, pneumatic or mechanical timing means for automatically controlling the three-way valve.
The foregoing known arrangements for alternately pressurizing and venting the gas chamber 6 of the bladder pump rely on a single air tube 14 extending down the well from the ground surface to the pump, a distance which varies from several feet to hundreds of feet. Actuating gas in the form of compressed air is conveyed to the pump via tube 14 to cause the pump to discharge, and the compressed air is then vented to atmosphere through the same tube 14 to cause the pump to refill. The volume of air tube 14 which must be filled and vented for each complete cycle of the bladder pump varies with the depth at which the pump is installed in the well.
The performance characteristics of the above known arrangements are limited by and dependent upon the depth at which the bladder pump is installed in the well. The actuation (pressurization) time for the directional air valve of the controller is dependent upon variables including displacement of the compressed air source, lift and particularly the volume of air tube 14. Because 0.4333 psi per foot of lift is required to lift water, the entire air tube 14 must be charged to 0.4333 psi before the upper check valve 12 of the bladder pump will open to discharge water. Although this problem can be countered by reducing the diameter of tube 14 to reduce pressurization time, another problem arises. The time required for venting, i.e., de-actuation of the directional air valve, is dependent upon the head over the top of the pump intake (submergence), lift pressure, and the volume of air tube 14. To the extent that the diameter of air tube 14 is reduced, venting of the compressed air is constricted and valve de-actuation time is increased. Because venting time is reduced by maximizing the diameter of air tube 14, while pressurizing time is reduced by minimizing the diameter of air tube 14, any saving of time in one phase of the cycle will result in a loss of time in the other phase of the cycle.
The time required to complete a pumping cycle increases as the length of air tube 14 increases, imposing an undesirable limitation on the already limited pumping capacity of bladder pumps used in groundwater sampling applications.
Because the bladder pump is typically arranged such that the pump intake is disposed near the bottom of a groundwater monitoring well, the length of air tube 14 corresponds roughly to the depth of the well. In a monitoring well having a depth of 150 feet, for example, there will be approximately 150 feet of air tube which must be alternately pressurized to 0.4333 psi per foot of lift, and then vented, during each cycle of operation of the bladder pump. Because most monitoring wells are only two inches in diameter, the diameter of the bladder pump is limited and the volume of water capable of being pumped per cycle is correspondingly limited. The time consumed per pump cycle by having to alternately pressurize and vent the volume of air tube 14, together with the limited size of the pump, severely limit the pumping capacity attainable.
The present inventors have experimented with several different methods for increasing the limited pumping capability of a bladder pump in a groundwater sampling application. These methods include increasing the length of the bladder pump, varying the size of the water discharge porting and tubing, using a higher displacement compressed air source, modifying the controller, and/or varying the diameter of air tube 14. However, the effectiveness of each of these methods is limited by one or more factors, such as increased cost, decreased reliability, the confining dimensions of the well, etc. Moreover, regardless of which method is used, the improvement in pump performance is marginal relative to the extent that pump performance suffers by having to alternately pressurize and vent the full volume of air tube 14.
The present inventors experimented with different diameter air tubes 14 to determine the effect on pump performance of different air tube volumes. At a range of approximately 1 to 50 feet of lift, using 2.55 standard cubic feet per minute ("SCFM") at 100 psi air displacement, optimum performance was achieved using an air tube with approximately a 3/8" inside diameter ("I.D."). At a range of approximately 50 to 100 feet of lift, the optimum air tube I.D. was approximately 1/4". At lifts exceeding approximately 100 feet, the optimum air tube I.D. was approximately 3/16". These results demonstrated that air tube volume affects pump performance differently at different lift and submergence conditions.
It is apparent from these results that the detrimental effect on pump performance of alternately pressurizing and venting the full volume of air tube 14 can be mitigated to some extent by adjusting the diameter of the air tube according to depth. However, the disadvantage arises that a variety of different diameter air tubes would be required to accommodate pump installations of varying depths. It is considerably more desirable to have a standard sized air tube for use in all applications.
Another alternative for partially overcoming the detrimental effect on pump performance of alternately pressurizing and venting the full volume of the air tube is to increase the capacity of the compressed air source. The air in tube 14 is thereby displaced more rapidly during pressurization to enhance performance during this phase of the pump cycle. However, this measure increases energy output while doing nothing to improve the performance detriment suffered during the venting phase of the cycle. The time it takes for the full volume of air tube 14 to be vented will remain as a factor inhibiting pumping capacity regardless of the characteristics of the compressed air source.
In groundwater monitoring, where samples are typically collected only weekly, bi-monthly, or even bi-annually, the chemistry of the groundwater begins to change within a couple of hours of leaving the sub-surface environment and entering the monitoring well. It is thus necessary to remove stagnant water from the well before sampling. Under current protocols, from three to ten standing volumes of water in the well must be purged before representative samples can be collected. Purging operations are the most time consuming part of the sampling procedure, and may occupy up to 98% of the overall time required for sampling.
To expedite purging, a gas-drive pump is often employed due to the limited pumping capabilities of the bladder pump. Gas-drive pumps are also commonly employed for recovery operations. However, there is a direct air-water interface in a gas-drive pump because compressed air communicates with the water. If low molecular weight components are contained in the pump body, where they are compressed and rapidly vented, vapors will be emitted from the discharge tube. The vapors can be hazardous, even explosive, and are generally detrimental to the environment. States which rigidly enforce air pollution standards may thus require that there be no air-water contact when pumping certain types of material from the well.
The bladder pump would be ideally suited for purging and recovery operations were it not for its limited pumping capability. In a bladder pump, there is no air-water contact because the bladder separates the air from the water in the pump. Thus, the venting of dangerous and environmentally harmful vapors throught the discharge tube is entirely eliminated.
The present invention greatly enhances the performance characteristics of the conventional bladder pump by eliminating the need to alternately pressurize and vent the large volume of air in tube 14 during each pump cycle. To this end, the invention provides the cycling means for the bladder pump at the pump itself, rendering the pump self-cycling. A bladder pump according to the invention is suitable for high flow-rate applications such as purging or recovery operations, and will hold pump performance substantially constant regardless of the depth of the well.